1. Field of the Invention
The present invention relates to methods of feeding dampening water in a printing machine.
2. Description of the Related Art
In a printing machine, the feed rates of dampening water and ink have a crucial influence on printing results. It is therefore necessary for the printing machine to adjust the feed rates of dampening water and ink properly.
To execute a method of automatically detecting the quantities of dampening water and ink and controlling the feed rates thereof, an apparatus has been proposed, for example, that measures a film thickness of ink and a film thickness of water on an ink kneading roller by using an infrared sensor or the like. However, such an apparatus presents difficulties in coping with environmental changes occurring in time of printing, and the apparatus itself is extremely expensive.
In Japanese Patent No. 2831107, a tone controlling apparatus has been proposed that detects densities of a solid portion and a halftone portion of a print, performs a comparison operation on the detected densities of the solid portion and halftone portion in relation to target densities of the solid portion and halftone portion inputted beforehand based on density variation characteristics of the solid portion and halftone portion occurring with variations in the feed rates of ink and dampening water, and simultaneously controls the feed rates of ink and dampening water based on results of the comparison operation.
There is a close relationship between the feed rate of dampening water and the feed rate of ink. As described in Patent No. 2831107, when the feed rate of dampening water and the feed rate of ink are varied simultaneously, the two influence each other and often fail to attain desired density values.
A printing machine has far more ink rollers for feeding ink to printing plates than water rollers for feeding dampening water to the printing plates. Thus, an adjustment of dampening water is reflected on printed matter in a shorter time than an adjustment of ink. As described in Patent No. 2831107, rather than adjusting dampening water and ink simultaneously, it is desirable to adjust the feed rate of dampening water first, and then to adjust the feed rate of ink while taking influences of the water adjustment into account.
Further, a printing machine can adjust the feed rate of ink for each predetermined area, but generally cannot adjust the feed rate of dampening water for each such area. However, the apparatus described in Patent No. 2831107 has, as a prerequisite, to adjust the feed rate of dampening water for each predetermined area. Such an adjusting method is difficult to implement with usual printing machines.
An object of the present invention, therefore, is to provide a method of feeding dampening water in a printing machine, that is capable of properly adjusting the feed rate of dampening water or ink.
The above object is fulfilled, according to the present invention, by a method of feeding dampening water in a printing machine for controlling a feed rate of dampening water along with a feed rate of ink by using first and second detecting patches printed adjacent each other on printed matter and presenting a difference in density variations after printing with varied feed rates of damping water and ink, the method comprising a density measuring step for measuring densities of the first and second detecting patches, a dampening water feeding step for controlling the feed rate of dampening water based on the densities of the first and second detecting patches measured in the density measuring step, and an ink feeding step for controlling the feed rate of ink based on the densities of the first and second detecting patches measured in the density measuring step, and the feed rate of dampening water.
In another aspect of the invention, there is provided a method of feeding dampening water in a printing machine for controlling a feed rate of dampening water along with a feed rate of ink by using two types of detecting patches printed adjacent each other in areas, L in number, arranged in a direction of width of printed matter and presenting a difference in density variations after printing with varied feed rates of damping water and ink, wherein one of the two types of detecting patches that has a large halftone area ratio comprises first detecting patches, while the other of the two types of detecting patches that has a small halftone area ratio comprises second detecting patches, the method comprising a critical density measuring step for measuring a critical density DM at which a shortage of dampening water causes a defective print, from prints obtained by performing printing a plurality of times while varying the feed rate of dampening water, a preparatory density measuring step for measuring a density D1x of the first detecting patches and a density D2x of the second detecting patches from each of prints obtained by performing printing a plurality of times while varying the feed rate of ink, a multiple linear regression step for deriving coefficients a, b and c from an equation (1) set out below and representing a parameter Dwx, by multiple linear regression, using the critical density DM measured in the critical density measuring step, and the density D1x of the first detecting patches and the density D2x of the second detecting patches measured in the preparatory density measuring step in time of each printing, a density measuring step for measuring a density D1x of each of the first detecting patches and a density D2x of each of the second detecting patches arranged in the areas, from printed matter obtained by trial printing, a parameter computing step for computing the parameter Dwx for each of the areas, by using the equation (1) set out below, from the coefficients a, b and c obtained in the multiple linear regression step, and the density D1x of each of the first detecting patches and the density D2x of each of the second detecting patches obtained in the density measuring step, a dampening water feed rate adjusting step for adjusting the feed rate of dampening water based on a minimum parameter minDwx of parameters Dwx for the areas obtained in the parameter computing step, an adjusted ink feed rate computing step for computing an adjusted ink feed rate a for each of the areas, by using an equation (2) set out below and representing the adjusted ink feed rate xcex1, from a target density DT, the critical density DM obtained in the critical density measuring step, the parameter Dwx for each of the areas obtained in the parameter computing step, and the minimum parameter minDwx of parameters Dwx for the areas obtained in the parameter computing step, and an ink feed rate adjusting step for adjusting the feed rate of ink for each of the areas based on the adjusted ink feed rate xcex1 obtained in the adjusted ink feed rate computing step:
Dwx=DMxe2x88x92D1x=axc2x7D1x+bxc2x7D2x+cxe2x80x83xe2x80x83(1) 
xcex1=DTxe2x88x92DM+(Dwxxe2x88x92minDwx)xe2x80x83xe2x80x83(2) 
In a further aspect of the invention, there is provided a method of feeding dampening water in a printing machine for controlling a feed rate of dampening water along with a feed rate of ink by using three types of detecting patches printed adjacent one another in areas, L in number, arranged in a direction of width of printed matter and presenting differences in density variations after printing with varied feed rates of damping water and ink, wherein one of the three types of detecting patches that has a large halftone area ratio comprises first detecting patches, another of the three types of detecting patches that has a smaller halftone area ratio than the first detecting patches comprises second detecting patches, and the remaining type of detecting patches that has a smaller halftone area ratio than the first detecting patches and a different resolution to the second detecting patches comprise third detecting patches, the method comprising a critical density measuring step for measuring a critical density DM at which a shortage of dampening water causes a defective print, from prints obtained by performing printing a plurality of times while varying the feed rate of dampening water, a preparatory density measuring step for measuring a density D1x of the first detecting patches, a density D2x of the second detecting patches a density D3x of the third detecting patches from each of prints obtained by performing printing a plurality of times while varying the feed rate of ink, a multiple linear regression step for deriving coefficients d, e, f and g from an equation (3) set out below and representing a parameter Dwx, by multiple linear regression, using the critical density DM measured in the critical density measuring step, and the density D1x of the first detecting patches, the density D2x of the second detecting patches and the density D3x of the third detecting patches measured in the preparatory density measuring step in time of each printing, a density measuring step for measuring a density D1x of each of the first detecting patches, a density D2x of each of the second detecting patches and a density D3x of each of the third detecting patches arranged in the areas, from printed matter obtained by trial printing, a parameter computing step for computing the parameter Dwx, by using the equation (3) set out below, from the coefficients d, e, f and g obtained in the multiple linear regression step, and the density D1x of each of the first detecting patches, the density D2x of each of the second detecting patches and the density D3x of each of the third detecting patches obtained in the density measuring step, a dampening water feed rate adjusting step for adjusting the feed rate of dampening water based on the parameters Dwx obtained in the parameter computing step, and an ink feed rate adjusting step for adjusting the feed rate of ink based on a target density DT, and the parameter Dwx obtained in the parameter computing step:
Dwx=DMxe2x88x92D1x=dxc2x7D1x+exc2x7D2x+fxc2x7D3x+gxe2x80x83xe2x80x83(3) 
In a still further aspect of the invention, there is provided a method of feeding dampening water in a printing machine for controlling a feed rate of dampening water by using two types of detecting patches printed adjacent each other on printed matter and presenting a difference in density variations after printing with varied feed rates of damping water, wherein the two types of detecting patches comprise first detecting patches having a halftone area ratio at substantially 100%, and second detecting patches having a halftone area ratio at Kxc3x97100% (K being a coefficient larger than 0 and smaller than 1), the method comprising: a density measuring step for measuring a reflection density Ds of the first detecting patches and a reflection density Dm from the printed matter, a coefficient computing step for computing a coefficient N, by using Yule-Nielsen""s equation (4) set out below, from results of measurement obtained in the density measuring step, and a dampening water feed rate adjusting step for adjusting the feed rate of dampening water based on the coefficient N:
Dm=xe2x88x92Nxc2x7Log{1xe2x88x92K(1xe2x88x9210(xe2x88x92Ds/N))}xe2x80x83xe2x80x83(4) 
The above methods of feeding dampening water enable a proper adjustment of the feeding rate(s) of dampening water and/or ink.
Other features and advantages of the present invention will be apparent from the following detailed description of the embodiments of the invention.